Spark plug



July 6, 1943-- A. G. CATTANEO SPARK PLUG Original Filed May 17, 1940 F e W .T m m 5 2 y W z u n x m" M C u .l G. m 1 9 M G w F mH mm 5 2 M58 8 3 I 7 8 2 l 2 E B y p O m m m n qU .m a r n m .l-nl FD lated manner.

Patented July 6, 1943 SPARK PLUG Alfred G. Cattaneo, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Original application May 17, 1940, Serial No. 337,416.. Divided and this application March 23, 1942, Serial No. 435,791

6 Claims.

The present invention relates to an improvement in ignition systems for internal combustion engines and particularly to a method and apparatus for cooling the central electrode of spark plugs of internal combustion engines utilizing spark ignition.

It is known that when spark ignition engines are heavily loaded in operation, the electrodes of the spark plugs may become suiliciently overheated to cause pro-ignition, detonation and similar forms of uncontrolled combustion. This trouble is encountered especially'with gasoline aero engines, particularly owing to the central electrode, for this electrode must be electrically insulated from the body of the spark plug by means of materials which in most instances are also heat insulators. Whereas the body of the spark plug can be cooled by metal fins which are exposed to the air, this is not the case with the central electrode, since the latter is not only largely enclosed in the body of the spark plug, but the projecting part is frequently surrounded by a radio screening device as Well.

It is also known that a large part of the ignition troubles encountered in aircraft engines and formerly attributed to faulty spark plug operation has in reality been caused by the high tension cables leading from the current source to the spark plugs due to the presence of moisture in the cable harness, the tendency to high tension cable breakdown at high altitudes, and other factors which tend to permit at least a temporary short circuit between the grounded metal harness and the cables themselves.

It is an Object of the present invention to provide a system and apparatus whereby both of these common difilculties are overcome in a re- Further, it is an object oithe instant invention to provide a spark plug of improved design, particularly suitable for use ac.- cording to the system to be described. Still further, it is an object to provide means whereby these diificulties are overcome with but slight modification of equipment already normally existent in aircraft engines.

It has already been proposed to cool spark plug electrodes in internal combustion engines by making the electrodes hollow and drawing air from outside into the cylinders through the electrodes during the suction stroke of the piston. In this case the conduits leading from the atmosphere to the cylinder space through the electrodes must be provided with non-return valves of o'fi'esort or another to prevent air or combustion gases from being driven out during the compression and working strokes of the pistons. These valves constitute a weak point from an operating standpoint, since their failure to operate will have serious consequences.

In the method according to the present inven: tion a coolant, preferably air or other suitable gaseous materials such as carbon dioxide 01' exhaust gases, is passed through a hollow central spark plug electrode which is closed towards the cylinder space. The internal hollow electrode is therefore not in communication with the cylinder space, so that there can be no escape of hot combustion gases through the electrode. As a coolant, dry air is quite suitable; it is a satisfactory electric insulator and further, in the present case, will be supplied to the hollow electrode under pressure, the electrode being thus easily kept within the desired operating temperature range of 500 to 800 C.

It has also now been found that by pressurizing' the so-called harness, which consists of metallic tubing suitably formed and which serves to protect the spark plug cables, most of the heretofore encountered trouble with short circuiting between the harness and the cables may be eliminated. In the present invention air under pressure from a pressurized harness is utilized as a coolant for the central electrode of the spark plugs, as will be more clearly understood from the following description of the appended drawi s.

Figure I is a sectional elevation of a spark plug especially adapted for use according to the inventlon.

Figure II is a diagrammatic drawing of a pressurized harness as utilized according to the invention.

Referrin particularly to Figure l',-the spark plug comprises a-bushlng-shaped part i including an earthed electrode 2, a central body 3 with the central electrode 6, which is insulated by insulating material S, ta, bb, $10 from the body 3 of the spark plug. The part of the central body projecting from the cylinder is provided with cooling fins.

Electrode i is provided with a cavity extending to the bottom end thereof and a tube 6 is fitted within this cavity projecting to the bottom of the same, where it is-split and equipped with tongues bent outwards to center it as at l. The top of the tube 6 is widened and is subjected to the action oi the spring 8 which tends to urge the tube upwards. As a result the tube 6 is pressed against the hollow contact piece ii, which both establishes electric contact between the cen-' tral electrode 4 and the spark plug cable it and conveys cooling air to tube.6 from the space between cable I!) and the harness tube I I. Harness tube ii is fastened to the electrode .body 3 by means of a cap nut l2. Care must of course be taken"; that contact piece 9 is insulated with respect to the grounded portion of the spark plug. To this end the intermediate piece l3, provided with/air ducts i4, should be made on non-conductive material. 3 is provided with openings i5, through which the air which has passed through tube ,8 of the central electrode and then through the annular space around this tube can escape to the atmosphere. The hollow contact piece 9 is also provided with openings as at It to permit ingress of air to tube 6.

In Figure II, each cylinder as at 24 of a. radial aircraft engine is supplied with a spark plug 'l'i constructed as shown in Figure I. A harness lead as at H extends from each spark plug to the harness manifold 88. High tension cables lead from a distributor 2i through a sealed conduit 23 to the harness. manifold l8 and thence to eachspark plug through harness leads as at H. An air pump it including a unit ill for drying and cleaning purposes supplies compressed air through a sealed conduit 22 to the harness manifold I8. If the engine or auxiliary equipment already includes a source of compressed air, as for example in airplanes utilizing pressurized cabins or those wherein fuel injection for the engines is used, the supercharger in such cases compressing only air, the air pump i9 shown is not necessary.

In operation, sufiicient air is supplied to the manifold harness it and harness leads (as at H) to maintain a positive pressure upon the high tension cables to the spark plugs of approximately lbs. per square inch, this pressure having been found satisfactory for most operating conditions to inhibit short circuiting. The air pressure within the harness will of course depend upon the volume and pressure of air supplied to the harness as well as the resistance to air flow through the spark plugs. Therefore, in operating a given engine according to the invention the fiow resistance through the spark plugs should be modified (for example by'varying the size of the orifices at M, is or it) so that a sufficient amount of air is passed through the spark plugs for cooling purposes and at the same time enough resistance to air flow is provided to maintain the desired pressure in the harness around the high tension cables.

The conditions mentioned previously herein, 1. e., sufflcient air to control the spark plug temperature between 500 and 800 C. and at the same time maintain an approximate 5 lbs. per square inch pressure in the harness, will be found satisfactory in most instances.

This is a division of my co-pending application, Serial No. 337,418. filed May 17, 1940.

I claim as my invention:

1. A spark plug suitable for use in an ignition system for internal combustion engines wherein a pressurized harness is utilized to inhibit high tension cable breakdowntendencies comprising a bodymember including a grounded electrode, a hollow central electrode closed toward thefiring end, insulating means between said body member and said central electrode, conduit means between said central electrode and said pressurized harness whereby a gaseous coolant medium under pressure may be passed from s d Near its top, the central body pressurized harness through said central electrode, contact means formed of a conductive material between said conduit means and said cen' -tral electrode, said conduit means being formed in fiow communication with said central electrode.

2. A spark plug suitable for use in an ignition system for internal combustion engines wherein a pressurized harness is utilized to inhibit high tension cable breakdown tendencies comprising a body member including a grounded central electrode, a hollow central electrode within said body member closed toward the firing end, insulating means between said body member and said central electrode, a conduit disposed within said central electrode andterminating at a point spaced from the closed end of said: central electrode, means for supplying a gaseous coolant under pressure from said pressurized harness to said conduit, an atmospheric vent in said body member in flow communication with said central electrode, means for supplying an intermittent high tension current to said central electrode and contact means formed of a conductive material between said conduit and said central electrode.

3. A spark plug suitable for use in an ignition system for internal combustion engines wherein a pressurized harness is utilized to inhibit high tension cable breakdown tendencies comprising a body member including a grounded central electrode, a hollow central electrode within said body member closed toward the firing end, insulating means between said body member and said central electrode, an atmospheric vent in said body member in fiow communication with said central electrode and means for supplying a gaseous coolant under pressure from said pressurized harness to said central electrode, said means being formedof a conductive material whereby a circuit is established between a high tension cable within said pressurized harness and said central electrode.

4. A spark plug suitable for use in an ignition system for internal combustion engines wherein a.

pressurized harness is utilized to inhibit high tension cable breakdown tendencies comprising a body member including a grounded central electrode. a hollow central electrode within said body member closed toward the firing end, insulat means between said body member and said central electrode, an atmospheric vent in said body member in flow communication with said central electrode, a conduit of lesser external diameter than the internal diameter of the central electrode disposed within said central electrode and terminating at a point spaced from the closed end of said central electrode, contact means between said conduit and said central electrode, conduit means between said conduit and said pressurized harness whereby a gaseous coolant may be passed from said pressurized harness to said conduit, said conduit, said contact means and said conduit means being formed of a conductive material whereby a circuit is established ing end, a tube of lesser diameter than the inside diameter of said central electrode extending within the bore of said central electrode andterminating at a point spaced from the closed end of said electrode, insulating means between said body member and said central electrode, a connecting piece between said tube and said pressurized harness whereby a gaseous coolant under pressure may be passed from said pressurized harness to said tube, an atmospheric vent in the upper portion of said body member in communication with said central electrode, spring means in contact with said central electrode and normally urging said tube against said connecting piece, said tube, said connecting piece and said spring means all being formed of conductive material whereby a circuit is established between whigh tension cable within said pressurized harness and said central electrode.

ALFRED G. CA'I'IANEO. 

